Electric furnace utilizing consumable electrodes and method of operating same



Feb. 28, 1961 ELECT Filed Nov. 22. 1957 R. J. GARMY 2,973,452 RIC FURNACE UTILIZING CONSUMABLE ELEcTRoDEs AND METHOD oF OPERATING SAME 16 Sheets-Sheet 1 INVENTOR. 5055/67 f 6AM/1V BJ. AJ.

Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE UTTLIZTNG CONSUMABLE ELEcTRoDEs AND METHOD oF OPERATING SAME Filed Nov. 22, 1957 16 Sheets-Sheet 2 F-IU j Wiz/f7 :i -Xlr IN VENTOR. OE/e J 64mm/ BUT. /J )4M A TTU/@NE V Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE -UTILIZING CONSUMABLE ELECTRODES AND METHOD OF OPERATING SAME Filed Nov. 22, 1957 16 Sheets-Sheet 5 Arran/fr Feb. 28, 1961 J. GARMY ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF `OPERATING SAME XXI Z7 Z7 o 16 Sheets-Sheet 4 f3.5@ if N o w am INVENTOR. Of/af GAR/W /77'70/9/VEY Feb. 28, 1961 ELECTRIC Filed NOV. 22. 1957 Fi E.

R. J. GARMY 2,973,452 FURNACE UTILIZING CONSUMABLE ELEOTRODES AND METHOD OF OPERATING SAME 16 Sheets-Sheet 5 INVEN TOR. 05527 6M/W B-J. Al.

Feb. 28, 1961 R. J. GARMY 2, 73,452

ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF OPERATING SAME Flled Nov. 22, 1957 16 Sheets-Sheet 6 Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD oF OPERATING SAME 16 Sheets-Sheet '7 Filed Nov. 22, 1957 1E. FE

INVENTOR. @5f/e7 J A/wy Arme/Vfl Feb. 28, 1961 R J. GARMY 2,973,452

ELECTRIC FURNCE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF OPERATING SAME Filed Nov. 22. 1957 16 Sheets-Sheet 8 BY w. H. wlw-auf ATTO//EV R. J. GARMY 2,973,452 ACE UTI NG coNsUMABL LEcTRoDEs D METHOD Feb. 28, 1961 ELECTRIC FURN AN Filed Nov. 22, 1957 OPERATING S 16 Sheets-Sheet 9 INVENTOR/ @055W Jn/wy Br Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF OPERATING SAME Filed Nov. 22, 1957 16 Sheets-Sheet 10 Fia-ES-A Feb. 28, 1961 ELEC R. J. GARMY TRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF OPERATING SAME Filed Nov. 22. 1957 16 Sheets-Sheet 11 'Br /J LPM Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF OPERATING SAME Filed Nov. 22, 1957 16 Sheets-Sheet 15 Br, ,0. www? Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD 0E OPERATING SAME Filed Nov. 22. 1957 16 Sheets-Sheet 14 INVEN TOR. amr f @f7/EMV ATTORNEY Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC EURNAOE UTTLTZTNC CONSUMABLE ELECTRODEs AND METHOD OF OPERATING SAME Filed Nov. 22, 1957 16 sheets-sheet 15 BUE Az.

Feb. 28, 1961 R. J. GARMY 2,973,452

ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OF' OPERATING SAME Filed Nov. 22. 1957 16 Sheets-Sheet 16 INVEN TOR. Of/Q f @www United ,seres Patent ELECTRIC FURNACE UTILIZING CONSUMABLE ELECTRODES AND METHOD OFF OPERATING SAME Robert J. Garmy, Canton, Ohio, assigner to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Filed Nov. 22, 1957, Ser. No. 698,256

6 Claims. (Cl. S14-69) titled Method and Apparatus for Forming Ingots, now

U.S. Patent No. 2,800,519, issued July 23, 1957.

This inventon relates to electric furnaces and particularly to furnaces for producing metallic ingots of high purity. The furnace described herein was designed especially for use with and has successfully been used with metals such as titanium, zirconium and the like, Which are diicult to melt because of their high meltingV points and also because of their high chemical activity at their melting points. This furnace has also been successfully used with other metals, e.g., steel, where an ingot of high purity was desired.

A problem of particular difficulty in connection with furnaces for use in the melting of titanium and the like is Ithe problem of safety with respect to the persons controlling the operation of the furnace and loading and unloading it. The extremely high operating temperatures involved, in the neighborhood of 3l40 F. (the melting point of titanium) and the great chemical activity of metals such as titanium and zirconium at their melting points make the probability of an explosion extremely high if oxygen, air or Water is allowed to leak into the furnace. Furthermore, if the structural parts of the furnace (which are commonly made of other metals having lower melting points) become overheated, those parts are likely to be destroyed,fwith resultantcontact between the molten titanium and air or water.

Another difficult problem in connection with such furnaces is the difficulty of lloading them. The furnace described herein is fed with consumable electrodes formed of titanium and/or other metal to be treated. For eX- ample, these electrodes may be compressed from titanium.

sponge and/or scrap by themethod and apparatus described in the copending application of Thomas A. Sindelar, Serial No. 571,810, iiled March 15, 1956, 'entitled Consumable Electrode Billets and Method and Apparatus for Making the Same. These electrodes are melted in the furnace by means of an are sovthat the electrode itself must carry heavy electrical current. In loading such an electrode into the furnace, it is necessary not.

Although continuously fed furnaces have been suggested, so far as is known, all commercially successful furnaces up to the present, including the furnace disclosed herein, have been batch furnaces, using electrodes of finite length.

Titanium ingots are being produced in increasingly large sizes. ln a batch type furnace, which must be shut down after each electrode is consumed for the insertion of a new electrode, the size of ingot which can be produced is limitedv by the size of electrode which can be fed. Consequently, increasingly larger electrodes are being used to produce the larger ingots, and the problem of supporting such electrodes is becoming increasingly ditlicult. y,

1t has been the practice in the past to control the feeding of the electrode, in a furnace of the type described, so as to maintain a substantially constant arc voltage. Since the arc voltage is subject to rapid fluctuations, a feeding system of that type requires frequent reversal of the electrode driving motor. Such a system involves a severe stress and indeed even shock to the electrode supporting and driving mechanism with each reversal, and may result in breaking a weak electrode, or shaking it loose from its support.

An object of the present invention is to provide an electric furnace of the type described which is considerably improved from the standpoint of safety. In this connection, an object of theinvention is to provide improved safety building structure for housing such a furnace; another object is to provide improved control land opera-tional features for such a furnace; and to provide improved signal and alarm devices for giving to anV voperator a signal of incipient unsafe conditions in the furnace.

' Another object of the invention is to provide improved apparatus for loading a consumable electrode into a furnace of the type described and for making electrical contact to such an electrode.

Another object of the invention is to provide improved mechanism for supporting an electrode in the furnace and for feeding it to the arc.

I Another object is to provide an improved method of operating the furnace, including particularly an improved met-bod of control of the rate of feed of the electrode.

The foregoing and other objects of the invention are attained, in the furnace described herein.

' The furnace includes a crucible mounted on a truck for horizontal movement along a set of rails. The crucible is supported on the truck by means of a set of jacks so that it may be raised `and lowered on the truck. When in its operating position, the crucible is raised on the truck so that its upper end sealingly engages the periphery of an opening in the bottom of a furnace shell.

Mounted on the upper end of the shell is a vertically elongated electrode receiving tube. The electrode supporting mechanism is located above the electrode receiving tube and -includes a power tube which extends through a seal in a cover at the top end of the electrode receiving tube and is vertically slidable in that seal.

The mechanism for supporting and feeding the electrode includes a clamp for engaging an end of the electrode. The clamp serves both as a support and as a means `for conducting electric current to the electrode. The clamp is removably fastened to a contact plate lolacted at the bottom end of the power tube which extends upwardly throughthe cover o-f the electrode receiving tube." The upper end of the power tube is attached by means of terminals and cables to a power supply. The power tube hangs Ifrom a crosshead which moves on two vertically extending lead screws. The lead screws hang from a crossbar mounted on two vertical masts. The lead screws are driven concurrently by a motor and suitable connecting gears and shafts. The entire supporting mechanism, including the motor, the masts, the crossbar, the crosshead, and the power tube and related parts are mounted on a carriage which is movable horizontally and located just below the level of the upper end of the electrode receiving tube. This carriage may be moved between an operating position in which the power tube is aligned vertically with the electrode receiving tube and a loading and unloading position in which the power tube and all the support mechanism are displaced horizontally from above the electrode receiving tube to permit the insertion of a new electrode by means of a crane or the like.

amants Each electrode clamp is vprovided with means, for

example, horizontal holes, through which rods may be;

inserted to support it temporarily on the top of the electrode tube. When loading a new electrode, 'the cover is removed from the electrode receiving tube and is lifted ,A

upwardly on the contact plate at the lower end of the power tube. The rods are inserted through the clamp to hang the old clamp and the stub end of the old electrode on the power tube. The contact plate is then disconnected from the clamp and lifted away vertically. rI'he entire supporting mechanism including the carriage then moves horizontally to clear the space above the electrode receiving tube. The old clamp and stub electrode can then be removed by a crane. A new electrode with a clamp attached to its upper end is then inserted in the electrode receiving tube by means of the crane, and is hung on the upper end of the tube by means of inserted rods. The crane and its cables are then unfastened and taken away. The carriage is then restored to its operating position and the contact plate is fastened -to the new clamp by means of nuts and bolts. The new electrode is then raised slightly to permit the removal of the temporary supporting rods, and the power tube is then lowered to bring the cover into place. After the `cover is fastened, the furnace is ready to proceed with 4further steps preliminary to a melting operation.

The atmosphere inside the furnace is maintained at a high vacuum during operation. An inert gas is supplied tothe furnace to maintain the vacuum at its desired value. the furnace is controlled by a pressure regulator at the gas supply.

The feeding of the electrode to the arc is controlled in accordance with a feature of the invention so as to feed the electrode at a substantially constant rate irrespective of minor fluctuations in the arc voltage. A safety control is responsive to the arc voltage and interrupts the operation of the feeding mechanism in the event that the arc voltage goes so high that an interruption of the arc is indicated.

A novel cooling system is provided including a pump supplying a high capacity recirculating system. In the event of failure of the pump, provision is made to cut off the supply of arc current and to transfer the water jackets to a lower capacity standby system which is sufficient to cool the jackets during a cooling down period of furnace operation.

Various safety controls are provided for cutting oft' the supply of current to the arc in the event that any of a plurality of conditions related to the furnace operation approaches a dangerous value. Such conditions include: the rate of ow' of water in water jackets, water supply pressure, furnace pressure, etc.

Various safety signals are provided, some responsive to certain of the operating conditions mentioned above and others responsive to less critical conditions, including for example, the water temperature in the cooling jackets. Controls for the vacuum or subatmospheric pressure inside the furnace and controls for the current in a stabilizing coil are provided by which an operator can terminate a glow discharge condition in the fur- The vacuum or subatmospheric pressure inside nace which has been indicated to him, for example, by a rise in the cooling water temperature.

The entire furnace is housed in a building structure so that the crucible and its supporting truck are located'. in a pit substantially below the ground level. shell is at or slightly below the ground level, and the electrode receiving tube projects upwardly above the ground level. The length of the tube is determined by the length of the electrodes it is desired to utilize. The practice is to extend the tube upwardly for twelve 0r fifteen feet.

One side of the crucible chamber is an exterior wall of the building. This wall, called a blowout wall, is made structurally relatively weak, while all the other walls enclosing the crucible chamber are made relatively strong. The purpose of this arrangement is that if an explosion occurs in the chamber, the exterior wall is blown outwardly, allowing the force of the explosion to dissipate in that direction, rather than into the building. Outside the blowout wall there is formed a pit in the adjacent earth. The pit is open at the top and has a setback or terrace at the ground level, with a wall a few feet back from the edge of the'pit. The pit and the terrace arrangements serve to dissipate the force of the explosion and to direct it upwardly, rather than hori zontally against adjacent structures.

The controls, recording and indicating instruments, etc.r for the furnace are placed in a control chamber on the ground floor level and on the opposite side of a safety wall from the furnace, preferably being located at a console adjacent a window in that safety wall. A safety window cover is located below the window and is hinged to the wall so that inthe event of an explosion at the furnace, it will be blown upwardly and cover the window. The safety cover is` always between the window and the furnace. The furnace may be observed through the window by means of a mirror located above the window on the inner side thereof. The control room is provided with a safety exit passage leading through a wall of the building preferably on a side different from that on which the blowout wall is located.

Other objects and advantages of the invention will become apparent from the following description and claims, taken together with the accompanying drawings.

Inthe drawings:

' Fig. l is an overall elevational view of a furnace embodying the invention, and showing the parts in full lines in their operating positions and in their loading and unloading positions in dotted lines;

Fig. 2 is a side elevational view, on a larger scale, of the electrode feeding and supporting mechanism shown in Fig. l;

Figs. 3 and 4 combined show an elevational view of the furnace taken from the left as viewed in Fig. 1;

Fig. 5 is a cross-sectional view of the crucible and related parts;

Fig. 6 is a detailed view showing the crosshead and its related parts, similar to a portion of Fig. 4 but on a larger scale;

Fig. 7 is a detailed view on the same scale as Fig. 6, showing the power tube and its sealing connection through the cover of the electrode receiving tube;

Fig. 8 is a view on the same scale as Fig. 6, showing in section the lower end of the power tube and its connection to the electrode clamp;

Fig. 9 is a cross-sectional view on line IX-IX of Fig. 6, showing the terminal structure used on the power tube;

Fig. l() is a view partly in plan and partly in section on the line X-X of Fig. 8, showing the crosshead;

Fig. 1l is a sectional view on the line XI-XI of Fig. 10;

Fig. 12 is a fragmentary section on the line XII- XII of Fig. 2;

Fig. 13 is a plan view of the carriage and related parts of the electrode supporting mechanism;

Thev

' centnal openings.

on the line modified form of electrode clamp, showing it resting temporarily on the upper end of the electrode receiving tube, the latter being shown in section;

Fig. 18 is a cross-sectional view taken on XVIII-XVIII of Fig. 17;

Fig. 19 is a plan view of an electrode guide structure used inside the electrode receiving tube;

Fig. 20 is an elevational view of the guide structure of the line Fig. 19;

Fig. 21 is a cross-sectional view of the electrode receiving tube, taken on the line XXI-XXI of Fig. 4, showing the guide structure in-place and guiding an electrode;

Fig. 22 is a view similar to Fig. 20, showing a modified form of guide;

Fig. 23 is a somewhat diagrammatic illustration of the inert gas supply system and the pressure control system for the interior of the furnace;

Fig. 24 is a somewhat diagrammatic illustration of the water supply system for the cooling jackets of the furnace;

Fig. 25 is an electrical wiring diagram of a system for supplying current to the arc stabilizer coil and certain related signals;

Fig. 26 is a wiring diagram of certain signal control circuits;

1 Fig. 27 is an electrical wiring diagram showing the arc current supply system with the various safety controls for cutting off that current supply;

' Fig. 28 is an electrical wiring diagram of the motor control system for the electrode drive mechanism;

Fig. 29 is a plan view of a furnace and a safety building construction for the furnace, according to a feature of the invention;

f Fig. 30 is a cross-sectional view of the building and furnace of Fig. 29, taken .along the line XXX--XXX of Fig. 29; and

Fig. 31 is a cross-sectional view of the building and furnace of Fig. 29, taken along the line XXXI-XXXI of that figure.

Sec. 1,-General furnace structure-Figs. 1 to 5 These figures illustrate `an electric furnace which is generally indicated by the reference numeral 1. Many details of the furnace structure have been omitted from Fig. 1 for purposes of clarification. The furnace 1 comprises a Crucible 2 in which an ingot is formed during operation of the furnace, a generally cylindrical shell or housing 3 above the Crucible 2, and an electrode receiving tube 4 which projects upwardly from the shell 3. A truck 9 carries the crucible 2 and is movable between an operating position shown in full lines in Fig. 1 and a loading and 'unloading position shown in dotted lines.

There are three operating levels for the furnace 1. The lowest level comprises a crucible chamber 5 in which the orucible 2- and the truck 9 are located and from which the crucible =2 and the ingot formed therein are unloaded.

As best seen in Figs. 1 and 4, the truck 9 carries four jacks 27 which may be driven concurrently by means of `a motor 28 and suitable gearing, or may be operated individually by means of handwheels 29. The four jacks 27 support a platform 31, best seen in Fig. 5, comprising a steel bottom plate 31a, an electrically insulating plate 31b, `and an upper electrically conductive plate 31e. All three of the plates 31a, 31b, 31e have aligned The bottom of the crucible 2 rests on the platform 31. One edge of the plate 31e is provided with an extension on which is mounted a plurality of terminals 32 (Fig. 1) of any conventional construction and of heavy current carrying capacity. The terminals 32 are connected by a like plurality of flexible cables 33 to a like plurality of stationary terminals 34 mounted on a busbar 3'5. The cables 33 are long enough and have sufficient slack so that the truck 9 may move between its operating position, shown in full lines in Fig. 1, and its loading and unloading position, shown in dotted lines, Without disconnecting either the terminals 32 or the terminals 34.

The second operating level of the furnace 1 is the furnace chamber 20. On the oor of this chamber (shown as a steel grating) there is mounted the furnace shell 3. The shell 3 is of a considerably greater diameter than the electrode 36 which extends downwardly through that shell, and consequently provides a substantial annular space around a portion of the electrode as best seen v in Fig. 5. At the shell 3 various instrumentalities having to do with the control of the atmosphere inside the furnace are connected, as illustrated diagrammatically in Fig. 23. The shell wall is made'double to provide a water jacket 3a (Fig. 5) and its top or head is also double walled to provide a head water jacket 3b.

The electrode tube 4 is mounted on the head of the shel13 and extends upwardly therefrom a substantial distance, e.g., l2 to 15 feet. The electrode tube 4 is provided to enclose a consumable electrode such as shown at 36 in Fig. 5, which is being fed to the furnace to form an ingot 37 in the bottom of the crucible 2.

The electrode 36 may be of compressed titanium sponge as shown and claimed in detail in the copending application of Thomas A. Sindelar, Serial No. 571,810, filed March 15, 1956, entitled Consumable Electrode Billets and Method and Apparatus for Making Same.

It has become conventional in the making of titanium lingots to run the titanium through a two-step process. I n

the first step, an electrode of compressed titanium sponge,v

forming operations is to increase the purity and homoge` -neity of the final product. The melting down of the material in the arc is very effective to remove those impurities which are gaseous or volatile at the temperatures employed. Since these temperatures are in the neighborhood of the melting point of titanium, namely 3140 F., it may be seen that most impurities are thereby removed. The double operation results in an ingot of high purity and homogeneity. Since titanium is still quite an expensive metal, it is commonly used only where its peculiar heat resistant properties and high strength to weight ratio are of great advantage. Such properties are at their best when the metal or alloy is most nearly free of undesirable contaminants. Consequently, practically all the present demand for titanium and its alloys is for the highly purified forms which may best be manufactured by repeating the melting step.

In any ingot form-ing operation using consumable electrodes of finite length, there is left a short butt end of the electrode which may not be used without danger to the clamp structure and possible contamination of the ingot. These butt ends are used by welding them to the ends of other butts, or other electrode billets. The welding operation commonly used leaves a groove in the outer surface of the electrode, as shown at 36a in Fig. 5.

The ingots formed in the first melt are considerably shorter and more dense than the compressed billets which are supplied to that first melt. In order to provide an electrode of greater length for the second melt, it is com mon to weld together two or more of the short electrodes from the first melt. These electrodes also are characterized by grooves in their outer surfaces at the weld points, as shown at 36a.

The third4 or upper level of the furnace 1 has a oor 34 (shown as a steel grid) a short distance (two or three feet) below the upper end of the electrode receiving tube 4. This floor supports the electrode feeding and driving mechanism. That mechanism is all mounted on a carriage 38 which moves horizontally between an operating position shown in full lines in Fig. 1 and a loading and unloading position shown in dotted lines in Fig. l. Mounted on the carriage 38 are two upwardly extending masts 55 connected `at their upper ends by a crossbar 56 (Fig. 3). Two lead screws 39` depend from thrust bearings 57 carried by the crossbar 56. The lead screws 39 turn in nuts 110 which are xed against rotation on a crosshead 41. A power tube 42 depends from a thrust bearing 43 on the crosshead 41. Nearits upper end, the power tube 42 carries a bracket 44 to which are attached a plurality of heavy dutyterminals 45. The terminals 45 are attached to a like plurality of .heavy duty flexible electrical cables 46 (Fig. 1) whose opposite ends are attached to fixed terminals 47 located on a busbar 48.

The power tube 42 extends downwardly through a sealing mechanism 49 (Fig. 3) located on a cover 50 at the top of the electrode receiving tube 4. Below the cover 50, the power tube 42, as best seen in Fig. 5, carries at its lower end a contact plate 1 attached by means of bolts 52Ato an electrode cl-amp generally designated at 53 and described in detail below in connection with Figs. 14 to 16. The electrode clamp 53 engages the upper end of the electrode 36 and not only supports it but serves as a path for conducting electricity to it.

Sec. 2.-Crucble structure andsupport-Figs. I, 4 and 5 The crucible structure, the truck and the related mechanisms concerned with the loading and unloading of the crucible on the truck, and the unloading of ingot from the crucible, yare not part of the present invention, but are shown and described more completely and claimed in my copending application Serial No. 672,603, tiled July 18, 1957, mentioned above.

Furthermore, the `specific water jacket structures of the crucible form no part of the present invention, being described more completely and claimed in my copending application Serial No. 651,328, led April 8, 1957, also mentioned above. However, an understanding of the crucible structure and its related parts are necessary to a complete understanding of certain features of the present invention, particularly those features relating to safety controls and operating controls. For that reason, a brief description of the crucible and the methods of loading and unloading are supplied herein, as follows.

The crucible 2 comprises a generally cylindrical wall section 71 and a base `plate 72. The Wall section 71 comprises a copper, inner shell 71a and a steel outer shell 71b defining between them a water jacket 71c supplied through a series of inlets, one of which is shown at 74, spaced around the bottom of the jacket. The water jacket 71C has a plurality of outlets 83 peripherally spaced around i-ts upper end. The wall section 71 is provided at its lower end with an outwardly extending flange 71d which is attached by means of a plurality of peripherally spaced bolts 73 to the peripheral edge of the base plate 72.

The base plate 72 comprises a lower plate 72a and an upper plate 72b defining between them a water jacket 72C supplied through a number of spaced inlets 75 and having a central outlet 76.

When a crucible is in place on the platform 31 it rests on the` conductive plate 31e, `which conducts the electric `arc current from the crucible to the terminals 32.

As best `seen `in Fig. 5, there is Aprovided near the upper end .of the crucible vwall section `71 an outwardly ,pro-

jectingnage 77. On the ilange 77 rests an insulating ring 78. An insulating cylinder 79 encircles the upperv Sec. 3.-Unloadxng of crucible and ingot-Jigs. I and 5 After an ingot has been finished in the crucible and the arc current turned off, the water in the cooling jackets is allowed to run for a time long enough to reduce the ingot temperature so that it may be readily handled. The' ingot and crucible are then unloaded from the truck 9 by the following procedure.

The inlets 74 for the crucible wall water jacket and the outlets 83 for those jackets, as well as 4the inlets and outlets for the base plate water jackets, are provided with quick-disconnect .coupling 74a, l83a which may be readily removed when preparing to unload the crucible.

A stabilizing coil 84 is wound varound the `outside of the crucible wall section 7.1 and is provided with quickdisconnect .electrical ,couplings 85. This coil A,carries a relatively low current ascompared `to the current ilowing through the electrode and the ingot, and the disconnection of electrical conductors for these relatively small cur rents is a simple matter and requires little time.

After the ingot has cooled down to a desired temperature, the interior of the furnace isopen to the atmosphere by opening a relief valve, thereby breaking the vacuum; in the furnace. The jacks 27 are then operated to ,lower the crucible with .the ingot therein, bringing the upper end of the crucible downwardly away from the crucible shell to a position where .the upper end of the crucible clears the lower `end of the shell and the adjacent `floor structures. The motor 54 is then operated to drive the truck 9 to the left as shown in Fig. l to the dotted line position underneath an opening 86 in the floor of the,

furnace chamber 20. This opening may be normally closed during furnace operation by means of a manhole cover or the like.

After the truck has reached its unloading position, the bolts 73 are removed so that the wall section of the crucible s freed from the base section 72. The cooling of the ingot causes it to shrink away from the wall section ofthe crucible so that the latter section may now be readily lifted off by a crane 87, located at the top ofA the furnace chamber 20. After the wall section of the crucible is removed, the finished ingot is accessible and may be lifted out by the same crane and removed to the next stage of its manufacturing operation. The base section 72 of the crucible is now lifted off and the truck is then ready for the installation of another crucible which has been prepared to receive an ingot.

The new crucible has had its wall section assembled to its base section by means of the bolts 73 at another location and has a layer of titanium sponge deposited in the bottom of the crucible to assist in starting the arc. This layer may be an inch or so deep over the whole surface, rising in a cone 4to about two or three inches at the center of the crucible. The truck with the new crucible on it is then run back horizontally to the operating position and the crucible is then lifted by the jacks to bring its upper end into abutment with the lower end ofthe furnace shell. The quick-disconnect couplings are Yreestablishcd and the crucible is theuready to proceed with further steps preliminary to the next melting operation of the furnace.

It may be seen that in this unloading and loadingoperation, there ,is on separate action required .to make `or 

